removed a bunch of unused things (especially options) and updated the maxValue logic

Now, we can pass in a maxValue option to actually get the graph to go to at least 5, for example, even if none of our data goes that high.
Merge branch 'patch-3' of github.com:tianon/radar-chart-d3

* 'patch-3' of github.com:tianon/radar-chart-d3:
  removed a bunch of unused things (especially options) and updated the maxValue logic

Conflicts:
	src/radar-chart.js